X-ray tubes generally include a cathode and an anode disposed within a vacuum vessel. The cathode is positioned at some distance from the anode, and a voltage difference is maintained therebetween. The anode includes a target track or impact zone that is generally fabricated from a refractory metal with a high atomic number, such as tungsten or any tungsten alloy. The anode is commonly stationary or a rotating disc. The cathode emits electrons that are accelerated across the potential difference and impact the target track of the anode at high velocity. As the electrons impact the target track, the kinetic energy of the electrons is converted to high-energy electromagnetic radiation, or x-rays. The electrons impacting the target track also deposit thermal energy into the anode.
A relatively large percentage of the electrons that strike the target track of the anode backscatter from the anode surface and are therefore sometimes referred to as “backscatter” electrons. The backscattered electrons can re-impact the anode and produce off-focus x-rays that diminish x-ray image quality. This occurs to a high degree in a bi-polar x-ray tube where the anode is maintained at positive potential relative to ground and a significant fraction of backscattered electrons are pulled back to the anode. Additionally, the backscattered electrons can interact with other internal components of the x-ray tube transferring kinetic energy in the form of heat until all their energy is depleted. Excess heat generation adversely affects the durability of the x-ray tube and may also increase expense associated with providing additional cooling capacity.